KANSAS CITY, Mo. — The Royals’ bullpen saves the old joke for the late innings. This is when it lands best. Brian Flynn and Blaine Boyer will wait for rookie reliever Brad Keller to jog to the mound. They will watch him throw his array of 96 mph cutters and biting sliders and heat-seeking sinkers and changeups — yes, don’t forget about the changeup. And then one pitch will be objective filth, and a batter will swing and miss by a foot, and one of the two relievers will remark that the Arizona Diamondbacks must have the most loaded pitching staff in baseball.

“We just look at them like: ‘What were they thinking?’” Boyer says.

“We say that every time he throws,” Flynn says. “’What are these guys doing right now?’”

It was the Diamondbacks, of course, who failed to protect Keller on their 40-man roster last winter. It was the Diamondbacks who watched him get scooped up by the Royals in the Rule 5 draft. It is the...